1. Field of the Invention
The present invention relates to a hydrostatic machine which includes a housing having an internal space accommodating a rotatably journaled driving mechanism, and wherein the portion of the internal space which is not occupied by the driving mechanism encompasses a drain oil chamber which receives the drain oil inclusive of lubricating oil which is discharged from bearing locations of the hydrostatic machine, and which is connected or port to a tank through at least one drain oil connection of the housing and through a drain oil line.
2. Discussion of the Prior Art
Hydrostatic machines of this type operate in accordance with the kind of construction thereof, at an overall degree of efficiency which lies within the range of about 75% to about 93%, and which is equal to the product obtained from the volumetric efficiency and from the hydraulic-mechanical efficiency.
The volumetric efficiency encompasses the drain oil losses which are encountered from the flows of drain oil produced and discharged from the internal oil circulation between the high-pressure and low-pressure sides of the hydrostatic machine, especially from the high pressure side thereof, and which collect in the drain oil chamber, and wherein these increase with an increasing speed in the rotation of the driving mechanism and a rising pressure differential between the high-pressure side and the drain oil chamber. As is known; for example, from the disclosure of U.S. Pat. No. 4,515,067, portions of these flows of drain oil are employed for the supplying of lubricating oil to the hydrostatic machine, in that they are conducted through the hydrostatic and/or mechanical bearing locations thereof before passing into the drain oil chamber.
The hydraulic-mechanical degree of efficiency is obtained from the hydraulic and from the mechanical losses. The hydraulic losses increase with an increasing speed of rotation of the driving mechanism, and incorporate a loss constituent which is dependent upon the density of the pressure medium, and a viscous loss constituent which is dependent upon the dynamic viscosity of the pressure medium. The mechanical losses are obtained from the increasing piston friction and bearing friction of the hydrostatic machine which emanate from the rising pressure differential.
Inasmuch as the overall degree of efficiency, as already mentioned hereinabove, is the product from the volumetric and hydraulic-mechanical efficiency, there is ascertained that both of these last-mentioned degrees of efficiency influence each other conversely. For example, an improvement in the hydraulic-mechanical behavior or property necessarily signifies a reduction in the friction losses and, inasmuch as this, in the main, can be constructively achieved only through an increase in the operationally-caused leakage gap and the tolerances of the hydrostatic machine, there is also concurrently encountered an increase in the drain oil losses and; respectively, a deterioration in the volumetric efficiency.